Presently, hot wire type flow meters are used in the internal combustion engine industry for measuring air flow into such engine. One such hot wire type air flow meter is disclosed in U.S. Pat. No. 4,974,445 issued to Arai et at. wherein the hot wire type air flow meter is used to detect and control the quantity of intake air into an internal combustion engine. Therein, it is noted that the hot wire type sensor is positioned within an intake air passage for obtaining an output signal corresponding to the total quantity of intake air by detecting the air flow velocity at this particular point. However, it is noted that the air passing over the hot wire sensor is not pressurized, thus, merely providing a single mesh screen at the inlet port leading to the flow meter is sufficient to reduce disorder from the air flow stream.
However, as can be noted from FIG. 7, when such a sensor is utilized in the fuel flow passage of a compressed natural gas internal combustion engine, significant noise is experienced to the point where the signal generated by the gas mass flow sensor is unusable.
Clearly, there is a need for a gas mass flow sensor for use in the fuel flow passage of a compressed natural gas fuel injected internal combustion engine wherein the quantity of gas passing through such fuel flow passage can be accurately detected by a hot wire type sensor thus generating a usable signal indicative of the flow of compressed natural gas passing therethrough.